Use all available nameservers in lookupIP

Some systems may be configured with public DNS only, so relying solely
on LAN servers could make the lookup process failed unexpectedly.

config_internal_test.go

@@ -2,12 +2,16 @@ package ctrld
 
 import (
 	"net/url"
+	"os"
 	"testing"
 
+	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestUpstreamConfig_SetupBootstrapIP(t *testing.T) {
+	l := zerolog.New(os.Stdout)
+	ProxyLogger.Store(&l)
 	uc := &UpstreamConfig{
 		Name:     "test",
 		Type:     ResolverTypeDOH,

resolver.go

@@ -367,6 +367,7 @@ func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string)
 		or = newResolverWithNameserver(defaultNameservers())
 	}
 	nss := *or.lanServers.Load()
+	nss = append(nss, *or.publicServers.Load()...)
 	if withBootstrapDNS {
 		nss = append([]string{net.JoinHostPort(controldBootstrapDns, "53")}, nss...)
 	}